The present invention relates generally to device processing and, in particular, to the planarization of non-planar surfaces in the fabrication of semiconductor or other devices.
The fabrication of electronic devices, such as semiconductor devices, typically produces surfaces that are non-planar. In some fabrication techniques, for example, multiple layers are formed sequentially on a silicon or other substrate. The layers can be processed into a desired pattern by the selective deposition of one or more materials or by removing selected regions of one or more layers. As more layers are formed, the topography or irregularity of the surface tends to increase.
An irregular surface can present various difficulties during device fabrication. For example, lithographic processes are often used to provide the patterning for the layers. During a typical lithographic process, a photosensitive material is deposited on a layer, exposed to radiation in a desired pattern, and developed to reveal the exposed pattern. To produce a photolithographic pattern with high resolution, the exposure light is focused at a specific depth, and the focus is maintained over a range of depths that is at least about two times the width of the pattern features. However, if the deposited resist material is not planar, the exposed image will not be in focus across the entire semiconductor wafer and throughout the film thickness. The likelihood of degraded lithographic results increases. Moreover, surface irregularities adversely affect metallization and other interconnections because the metal deposited over the surface has bends and turns which conform to the surface irregularities. Such bends and turns can cause undesirable current crowding.
To reduce the effects of surface irregularities, techniques are used to planarize the surface of the device on which the photosensitive material is deposited. Such techniques include, for example, etch-back techniques as well as chemical-mechanical polishing (CMP) techniques.
Recently, a technique has been proposed in which an object with a flat surface is pressed into contact with a planarization material, such as a photoresist or resin, deposited on the wafer. The planarization material is cured while in contact with the flat surface, and the flat surface is separated from the planarization material. The planar surface then can be transferred from the planarization material to the underlying layers.
One difficulty encountered with the foregoing technique is that, when the flat surface is separated from the planarization material, the planarization material can adhere to the flat surface, resulting in a surface that is less planar than desired. Accordingly, it would be advantageous to have a technique for planarizing a substrate in a manner that reduces or prevents adhesion of the planarization material to the flat surface.